On June 11, 1991, a Bell 47G3B1 (registration N73284) operated by Tery Jon Aviation was involved in an aviation accident near Lasalle, MN. Investigators recorded the probable cause as: The pilot's decision to fly the spray swath at an insufficient altitude, resulting in the spray boom contacting the crop. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive; 1 related events involving the same aircraft type or operator are linked below.
A helicopter conducting aerial application operations struck a wheat field with its spray boom during the first pass, causing the aircraft to crash and land inverted. The pilot survived the incident.
What happened
The accident occurred while the pilot was engaged in aerial application operations over a wheat field. At the time of the event, the pilot was executing the initial spray swath across the target area. During this low-altitude maneuver, the helicopter's spray boom made contact with the crop canopy. The impact caused the aircraft to lose control and strike the ground. Upon impact, the helicopter came to rest in an inverted position.
The investigation
Post-accident examination of the site confirmed that the primary point of failure was the interaction between the spray equipment and the vegetation. The mechanical integrity of the helicopter's flight controls was not cited as a contributing factor in the narrative provided. The physical evidence supported the conclusion that the low-level flight path resulted in the collision.
Findings
The investigation identified the specific operational error leading to the crash. The pilot was flying too close to the ground for the equipment configuration being used. The contact between the spray boom and the wheat crop initiated the loss of control. To prevent recurrence, it is recommended that pilots conducting similar aerial application tasks maintain a higher altitude during spray swath operations to ensure adequate clearance from obstacles and terrain.
Probable cause
The pilot's decision to fly the spray swath at an insufficient altitude, resulting in the spray boom contacting the crop.